The present patent application herein specifically refers to and incorporates in its entirety the disclosed by Gary Lennen U.S. patent application Ser. No. 08/943,552, entitled "CALIBRATION FOR CODE GROUP DELAY ERRORS IN RECEIVERS", filed on the same date as the present patent application, and assigned to the assignee of the present patent application.
Code phase (also known as pseudo-range) measurements are now commonly processed successfully in GPS Receivers to provide high accuracy position, velocity and time measurements, e.g. in differential and surveying applications. Numerous error sources in these measurement have been revealed and techniques have been developed to minimize or completely eliminate these errors. The U.S. Pat. No. 5,526,291, issued to Lennen, discloses how to solve the error in code and carrier phase caused by different Receiver designs reacting differently to the same satellite signal because the different Receiver types use different filtering, amplification and other components.
Lennen et al. in the U.S. Pat. No. 5,515,057, describes how errors in the code and carrier phase measurement caused by electrical asymmetries in the antenna element could be solved.
One important kind of the code phase error is caused by the group delay characteristics within a GPS/GLONASS Receiver. A combined GPS/GLONASS satellite positioning system Receiver was disclosed by Gary Lennen in the U.S. patent application Ser. No. 08/831,095, entitled "Combined GPS/GLONASS Satellite Positioning System Receiver", filed on Apr. 1, 1997 and assigned to the assignee of the present patent application. The U.S. patent application Ser. No. 08/831,095 is specifically referred to in the present patent application and is incorporated herein in its entirety.
The group delay code phase errors caused by variations in the group delay across the received bandwidth are due to the specific characteristics of filters, amplifiers and other active components in a GPS/GLONASS Receiver design. For instance, it is desirable for a GPS/GLONASS Receiver to include the specific filter and amplifier components that would allow for the substantial filtering of out of band signals to prevent possible jamming.
The code phase errors caused by the group delay characteristics within a satellite Receiver are more pronounced in a GLONASS Receiver than in a GPS Receiver. The GPS satellites transmit on the same nominal frequency. Thus, a GPS Receiver inflicts substantially similar and very small group delays (less than one centimeter) on the satellite signals emanating from each GPS satellite. Thus, the code phase errors caused by the group delay characteristics within a specific GPS Receiver can be largely ignored for most GPS-related applications.
On the other hand, the GLONASS satellites transmit and are received on different frequencies. When two GLONASS Receivers and two GLONASS satellite signal code phase measurements are differenced, in a double difference measurement, the group delay differences between the different GLONASS satellite signals can cause a substantial error (in the order of one meter code phase) that cannot be ignored for most GLONASS-related applications.
What is needed is the technique that would allow the satellite Receiver to maintain the active components with the specific desirable characteristics (like anti-jamming capabilities) while allowing the group delay code phase errors to be removed as an error source from the pseudo range measurements.